Single acting twin cylinder pump or compressor



July 18, 1967 H. BAUER 3,33

SINGLE ACTING TWIN CYLINDER PUMP OR COMPRESSOR Filed Aug. 23, 1965 2 Sheets-Sheet'l I I I 7 V I i I V 3 I l j I; l Li I I I I I I 5 I F I 1 FIG I I4 I, 13 T I FIG 2 INVENTQR l5 :70 Helmut Bauer wga/gnae ATTORN EYS July 18, 1967 SINGLE ACTING TWIN CYLINDER PUMP OR COMPRESSOR Filed Aug. 23, 1965 H. BAUER 3,331,329

2 Sheets-Sheet 2 J 7 2 ,29 FIG 3 i! 2/ 1 l i /7 l I J I l I a M 1% k III INVENTOR ATTORNEYS United States Patent 3,331,329 SINGLE ACTING TWIN CYLINDER PUMP 0R COMPRES0R Helmut Bauer, Basel, Switzerland, assignor to Masclzinenfahrik Eurekhardt AG, Basel, Switzerland, a Swiss corporation Filed Aug. 23, 1965, Ser. No. 481,470 'Claims priority, application Switzerland, Aug. 25, 1964, 11,099/ 64 4 Claims. (Cl. 10349) The invention relates to a single acting twin cylinder pump or compressor.

Pumps or compressors for very high pressure are often constructed with hydraulic drive, because this mode of drive makes it possible easily to deal with the high forces arising. Such hydraulic motors are usually of the kind in which a double acting hydraulic driving cylinder is arranged in the centre which at both ends actuates a respective high pressure piston. If the driving medium is supplied by a volumetric (i.e. positive displacement) pump which delivers at a constant rate independently of the terminal pressure, the piston moves during its stroke at a uniform speed and the high pressure medium is also uniformly delivered.

However, at the end of each stroke there is an interruption of the uniform delivery which could only be avoided if the reversal of movement at the ends of the stroke could take place instantly, because then delivery by the piston at the opposite end would continue directly after the delivery by the first piston without any delay in time. Such sudden reversal of the movement would involve, however, infinite acceleration and unsupportable pressure shocks in the driving medium piping. In practice therefore, such machines are constructed to work with a gradual reversal in order to keep the acceleration of the driving piston within reasonable limits. Accordingly the reversal takes a certain time and during this time the delivery by the high pressure piston is interrupted. Further, during the time of reversal the consumption of driving medium falls because the driving piston runs more slowly or momentarily comes to rest. As, however, the driving medium pump continues to run and to deliver at a constant rate there would again be a pressure shock in the driving medium piping if the time of the gradual reversal were made too great.

A purpose of the present invention is to mitigate these disadvantages and to provide a pump or compressor of the aforesaid kind having constant driving medium consumption so that the driving medium pump has no sudden pressure rises to overcome and consequently works without shocks. A further object is to arrange the high pressure part of the machine so that it gives practically uninterrupted uniform delivery. To these ends the invention essentially consists in the provision of two single acting high pressure cylinders and two driving pistons which can be driven alternately independently of one another while the flow of the driving medium from the pump serves only for effecting the working strokes of the driving pistons and the working strokes of the two pistons are so overlapped in time that the sum of the speeds of the driving pistons remains constant.

Further details will appear from a description of embodiments illustrated in the accompanying drawings, given solely by way of example.

In the drawings:

' FIGURE 1 is a diagrammatic section of a first embodiment of a high pressure pump or compressor.

FIGURE 2 is a graph of the conditions of motion in the embodiment of FIGURE 1.

FIGURE 3 is a diagrammatic section of another embodiment of a pump or compressor according to the invention, and

FIGURE 4 shows the slide valve of the embodiment of FIGURE 3 in its mid position.

In the example illustrated in FIGURE 1 a uniform flow of driving medium is produced by a volumetric driving medium pump 1, which flow in the position shown of the slide valve 2 is directed below the driving piston 3 so that the driving piston 3 moves upwards at uniform speed. In doing this the driving piston 3 actuates the high pressure piston 4 working in a cylinder not shown of a high pressure pump or compressor. The neighboring driving piston 5 moves downwards under the action of a spring 6 and forces the driving medium below it back into the reservoir. It is essential that the downward movement of the driving piston 5 by the spring 6 should take place faster than the upward movement of the riving piston 3 so that the piston 5 will already have come to rest at the lower dead point before the piston 3 has reached the upper dead point.

When the driving piston 3 approaches the upper dead point, by means of a mechanism not shown it displaces the slide valve 2 into its mid position in which flow of the driving medium from the pump 1 into both cylinders below the pistons 3 and 5 is made possible so that the movement of the piston 3 slows down and the piston 5 begins to move. Since the pump 1 delivers at a constant rate and the pistons 3 and 5 are of the same diameter, the sum of the piston speeds of the pistons 3 and 5 must remain always the same.

As soon as the piston 5 begins to move, through a mechanism not shown, it displaces the slide valve 2 into its other end position so that the flow of driving medium is now entirely beneath the piston 5 while the piston 3 commences its return movement under the action of the return spring.

It is an essential feature of this embodiment of the invention that the driving medium delivered by the pump 1 is used only to effect the upward movements of the pistons and that the downward movements of the pistons are effected by other means. It is by this feature that the result is obtained that the sum of the piston speeds of the pistons 3 and 5 always remains constant, and that the quantity of oil (driving medium) consumed by the pistons 3 and 5 remains constant so that no pressure shocks arise at the pump 1. Further the sum of the piston speeds of the high pressure pistons 4 and 7 which are also of equal diameters, is constant so that practically constant delivery of the high pressure medium being pumped is achieved.

The delivery of the high pressure medium would be completely uniform if neither the driving medium nor the high pressure medium were compressible and if the material used in constructing the machine were not elastic. In consequence of the compressibility of the media and the elasticity of the material there is a certain interruption in delivery but this is so small that in most cases it can be neglected because it is compensated by the elasticity of the pressure piping.

As already mentioned for the sum of the piston speeds always to remain constant the driving medium e.g. oil supplied by the pump 1 under high pressure must not be used for any other purpose than the upward movement of the pistons. Accordingly for the return movements of the pistons 3 and 5 according to FIGURE 1 return springs 6 are provided. Instead of such springs, however, other means could be used as, for example, compressed air cushions or oil pressure produced by another source.

' The details of the mechanism for moving the slide valve 2 is not the subject of the invention and can be formed by known means. Thus, for example, edge cams could be provided, on both piston rods which through rollers produce the required displacements of the slide valve at the ends of the stroke. Or control bores could be provided at suitable places in the cylinders through which at the beginning and end of the stroke pressure impulses are given which could be used to effect the desired displacement of the slide valve.

As according to the invention the movement of the one piston commences before the movement of the other piston has terminated, it is necessary as already mentioned that the return stroke should be effected faster than the working stroke. The conditions of motion which arise are graphically illustrated in FIGURE 2. In this diagram the stroke movement is plotted against time. From the point 8 to the point 9, for example, the space below the piston 3 alone is connected to the pump 1 and the piston therefore moves from 8 to 9 with uniform speed. When the point 9 is reached the slide valve 2 as above explained is displaced and the other driving piston 5 starts to move at the point 10. The first piston is therefore decelerated and comes to rest at the point 11 while the second piston has reached full speed at the point 12. The interdependence of the movements of the first piston from 9 to 11 and of the second piston from to 12 is such that the sum of the piston speeds must remain constant. From the point 12 to the point 13 the piston 5 now moves with constant speed under the effect of the constant delivery of the driving medium until at the point 13 the slide valve moves into the mid-position so that the piston 5 comes to rest at the point 14 while at the same time the first mentioned piston 3 commences to move at the point 15. The return movement of the second piston 5 from the point 14 to the point 10 must therefore take place faster so that at the point 10 it has already reached its lowest position. The piston speed during the greater part of the working stroke is given by the ratio s:t while the piston speed during the greater part of the downward movement must amount to at least s:!. If the piston speed during the downward movement is greater than necessary this has no disadvantage because the piston in any case remains at rest at the lower dead point until the piston effecting the working stroke reaches the point 9 or 13.

It is however easily possible by a further development to give the two pistons exactly the necessary speeds during the downward movements as well as the upward movements. For this purpose oil is used which during the upward movement of the driving piston is displaced above it in order to produce the downward movement of the other piston and an arrangement is provided by which the oil acts on a correspondingly small piston surface of the second piston and thus gives it a higher speed of movement.

An example of this construction is diagrammatically illustrated in FIGURE 3. Here again the driving medium pump is marked 1, which in the position shown of the slide valve 2 supplies the driving medium through the pipe 16 below the driving piston 3 so that this piston effects its upward movement with uniform speed.

The driving piston 3 is constructed as a stepped piston with respective surfaces 17, 18 on its upper side. In the position shown of the slide valve 2 the two cylinder spaces above the surfaces 17 and 18 respectively are connected together through the pipes 19 and 20 and during the upward movement the oil displaced by both these surfaces, through a connecting pipe 21 acts on the surface 22 only of the other piston 5. The connecting pipe 23 between the space above this surface 22 and the slide valve 2 is at this time closed by the valve. Accordingly the piston 5 moves downwardly faster than the upward movement of the piston 3, the sum of the annular surfaces 17 and 18 being to t as the annular surface 22 is to t. By appropriate choice of the relative diameters a desired speed relationship can be achieved.

During this period, the space above the annular surface 24 of the second piston 5 is connected through the pipes 25 and 26 with the space beneath this piston and during the downward movement the oil displaced by the difference between the respective surfaces of the piston can flow back through the bores 27 in the slide valve 2 into the return pipe,

FIGURE 3 also includes as another development that the piston rods 28 and 29 through which the movements of the driving piston are transmitted to the working pistons 4 and 7, are continued on the undersides of the pistons by counter-piston rods 30 and 31 of the same diameter which pass through stufling boxes to the outside. The result of this is that independently of the particular position of the pistons 3 and 5 and independently of the particular position of the slide valve 2 the total volume of driving medium in the system always remains constant and the apparatus can work in a closed circuit.

Working in a closed circuit is of particular importance when the invention is applied not to a pump but to a high pressure compressor.

If for example the machine works as a compressor and the piston 7 is effecting its suction stroke it is loaded by the suction pressure which in a high pressure compressor can have quite a high value.

Accordingly when the driving piston 5 moves downwardly an oil pressure is produced beneath it which is proportional to the suction pressure acting on the piston 7. This oil pressure proportional to the suction pressure is delivered through the pipe 33 to the pump 1. The pump 1 must generate a pressure which is proportional to the full final pressure on the Working piston 4. As this is not from the pressure in a reservoir but from the counterpressure in the pipe 33, the pump only has to overcome a pressure difference which is proportional to the pressure difference between the suction pressure acting on the piston 7 and the final pressure on the piston 4.

In order to avoid a penetration of air into the closed circuit this circuit is held continuously under an excess pressure by a small feed pump 35. The value of the excess pressure is determined by a safety valve 36 which allows a constant small flow of oil back into the reservoir.

The movement of the slide valve 2 in the embodiment of FIGURE 3 can be effected in exactly the same way as for that of FIGURE 1. Shortly before the driving piston 3 reaches its upper dead-point, by suitable mechanism it moves the slide valve into its midposition so that a passage for oil is opened into the space beneath the piston 5 as well as to that beneath piston 3 and the piston 5 is set in movement while the piston 3 moves down.

To enable this to be more easily followed this midposition of the slide valve 2 is shown in FIGURE 4. The fluid coming from the pump 1 through the pipe 34 in this position of the valve is admitted simu'taneously to the pipes 16 and 26 and therefore drives both pistons simultaneously in such a way that the sum of the piston speeds remains constant. The remaining pipes 20, 19, 25 and 23 in this position are connected to the return pipes 32 and 33 so that the upward movement of the two pistons is not hindered.

Shortly after the piston 5 starts to move it displaces the slide valve 2 to the other end position with the result that the oil which is displaced by the annular surfaces 22 and 24 acts solely on the annular surface 18 and this causes accelerated return of the piston 3.

The embodiment illustrated in FIGURE 3 like that shown in FIGURE 1 is only to be regarded as an example and can be modified in various ways without departing from the scope of the invention.

Thus, for example, it is possible not to connect the space above the annular surfaces 18 and 22 continuously through the pipe 21 but the space above the annular surfaces 17 and 24, the diameters again being made such that the required motion characteristic is obtained.

It is further possible to arrange the stepping of the piston surfaces which are necessary to achieve the different speeds on the working and return strokes not as in the drawing of the upper side but on the under side of the driving pistons.

In general, though, it is convenient to arrange the pistons and working cylinders side by side. This is not essential nor need the working stroke be upward and the return stroke downward.

What I claim is:

1. A high pressure pump or compressor comprising two single acting working cylinders, a working piston in each working cylinder, an independent driving piston driving each said working piston, means providing a constant supply of hydraulic pressure medium, means applying the supply of hydraulic pressure medium solely for effecting the working stroke of each driving piston, means controlling the flow of said medium so that the working strokes of said driving pistons are over-lapped in time and the sum of the speeds of said driving pistons remains constant, means for effecting the return strokes of the driving pistons at a higher speed than the working strokes, each driving piston having a smaller surface than the surface upon which said medium works during the working stroke, the surface of each driving piston opposite that on which said hydraulic medium acts, during the working stroke, displacing a liquid which acts on said smaller surface of the other driving piston to return it at a greater speed than that of the piston making its working stroke, the total liquid volume being constant independently of the position of said driving pistons and being contained in a closed circuit.

2. A pump or compressor as set forth in claim 1 wherein each driving piston is stepped to provide two annular surfaces on the opposite side of the piston to that on which said hydraulic medium acts during the working stroke, pipes which during the working stroke of each piston convey liquid displaced by both said annular surfaces to act on one only of the annular surfaces of the other piston and a further pipe which during the return stroke connects the space from which liquid is displaced by the other of said annular surfaces with the space to which said hydraulic medium is supplied during the working stroke, both said spaces being connected during the return stroke to the return pipe leading to the means for supplying said hydraulic medium.

3. A pump or compressor as set forth in claim 1 comprising a feed pump and safety valve, said feed pump maintaining said closed circuit under pressure and said safety valve determining the pressure maintained.

4. A pump or compressor as set forth in claim 1 wherein a slide valve controls the distribution of said hydraulic medium, said slide valve being controlled by said driving pistons so that when a driving piston approaches the end of its working stroke said slide valve is shifted into a mid position to supply said medium to both said driving pistons and when a driving piston starts its driving stroke moves said slide valve into a position in which the supply of medium to the piston which has completed its working stroke is cut 01f and is supplied to the piston which has just commenced its working stroke.

References Cited UNITED STATES PATENTS 2,274,224 2/1942 Vickers 103-49 2,453,929 11/ 1948 OHarah 103-49 X 2,660,955 12/1953 Kent et a1 103-49 X 2,799,444 7/1957 Schemrnel 230-53 2,866,415 12/1958 Montelius 103-49 ROBERT M. WALKER, Primary Examiner. 

1. A HIGH PRESSURE PUMP OR COMPRESSOR COMPRISING TWO SINGLE ACTING WORKING CYLINDERS, A WORKING PISTON IN EACH WORKING CYLINDER, AN INDEPENDENT DRIVING PISTON DRIVING EACH SAID WORKING PISTON, MEANS PROVIDING A CONSTANT SUPPLY OF HYDRAULIC PRESSURE MEDIUM, MEANS APPLYING THE SUPPLY OF HYDRAULIC PRESSURE MEDIUM SOLELY FOR EFFECTING THE WORKING STROKE OF EACH DRIVING PISTON, MEANS CONTROLLING THE FLOW OF SAID MEDIUM SO THAT THE WORKING STROKES OF SAID DRIVING PISTONS ARE OVER-LAPPED IN TIME AND THE SUM OF THE SPEEDS OF SAID DRIVING PISTONS REMAINS CONSTANT, MEANS FOR EFFECTING THE RETURN STROKES OF THE DRIVING PISTONS AT A HIGHER SPEED THAN THE WORKING STROKES, EACH DRIVING PISTON HAVING A SMALLER SURFACE THAN THE SURFACE UPON WHICH SAID MEDIUM WORKS DURING THE WORKING STROKE, THE SURFACE OF EACH DRIVING PISTON OPPOSITE THAT ON WHICH SAID HYDRAULIC MEDIUM ACTS, DURING THE WORKING STROKE, DISPLACING A LIQUID WHICH ACTS ON SAID 